1. Field of the Invention
This invention lies in the field of HABER ammonia synthesis apparatus. More particularly, it concerns the design of an improved means for supplying gases to the second reformer of a classical HABER ammonia synthesis apparatus. Still more particularly, it concerns the design of a conduit system for thoroughly mixing a combustible fuel, such as methane or natural gas, and steam in selected ratio with a major supply of air, all at selected temperature and pressure, prior to flow into the second reformer of a HABER ammonia system, to react therein with the hot products of combustion with the first reformer.
2. Background and Description of the Prior Art
The HABER process, which catalytically combines nitrogen and hydrogen for ammonia (NH.sub.3) synthesis is well-known in the chemical industry. Feed preparation for the HABER process must make both nitrogen and hydrogen in 1-3 volume ratio, respectively, available prior to synthesis.
Hydrogen is available, because of primary reforming, to catalytically combine hydrocarbon (CH.sub.4 preferably) with H.sub.2 O as CH.sub.4 +H.sub.2 O=CO+3H.sub.2, and the CO is later reacted to CO.sub.2 +H.sub.2 prior to synthesis, followed by CO.sub.2 removal, leaving only H.sub.2 for synthesis.
The N.sub.2 becomes available in a secondary reformer when a selected quantity of air (78.05% N.sub.2 +20.95% O.sub.2) is injected into the 1,500F gaseous effluent from the primary reformer which contains CO and H.sub.2. Because of the presence of O.sub.2, a portion of the CO and H.sub.2 burns to increase the gas temperature to the vicinity of 2,000F. Gases at 2,000F then pass into a second catalyst bed for conversion of any residual CH.sub.4 to CO.sub.2 and H.sub.2. There is a further processing prior to ammonia synthesis so that essentially N.sub.2 +3H.sub.2 proceed to synthesis. Thus, the secondary reforming air injection does two things: first, supplies N.sub.2, and second, elevates temperature due to burning as the O.sub.2 of the air encounters fuels which are significantly above fuel ignition temperature.
The burning of fuels is only partial for the total CO and H.sub.2 contents of the primary reformer effluent gases. Thus, it is required for the secondary reforming reactions via catalysis to convert residual methane or natural gas (CH.sub.4) to CO.sub.2 +2H.sub.2. However, this means for temperature elevation in the secondary reformer is wasteful of fuel. It is wasteful because, for each mol of methane or natural gas, which is reacted with water vapor to form CO and H.sub.2, fuels must be supplied to the primary reformer burners for the endothermal heat of reaction for CH.sub.4 +H.sub.2 O=CO+3H.sub.2 or 89,021 btu/mol of methane, which fuels are subsequently partially burned in the secondary reformer as CO+3H.sub.2 (Gas Engineer's Handbook, McGraw-Hill, First Edition, Seventh Impression). This means that, for each 1,000,000 btus of secondary reformer heat, there must be fuel burned to supply 1,000,000+(2.907.times.89,021)=1,258,000 btus, which is 1.258 .times. what it should be if methane, per se, could be used as secondary reformer fuel to replace the CO and H.sub.2 fuels burned, as the HABER process is now operated for ammonia synthesis in the chemical industry.
As has been discussed, each secondary reformer is equipped with air injection means to which selected air quantity is delivered at pressure greater than the pressure internal of the secondary reformer vessel.